Pandas fillna can't process np.float16 type

Code Sample, a copy-pastable example if possible

p_s = pd.Series(data=[47.97,   np.NAN,  np.NAN, 47.16, 47.97], dtype=np.float16, 
                index=pd.DatetimeIndex(['2015-07-24', '2015-07-25', '2015-07-26', \
                                                          '2015-07-27','2015-07-28']))
p_s
Out:
2015-07-24    47.96875
2015-07-25         NaN
2015-07-26         NaN
2015-07-27    47.15625
2015-07-28    47.96875
dtype: float16

Problem description

p_s.fillna(method='ffill') get the error: ValueError: Invalid dtype for pad_2d [float16] But: p_s.astype(np.float64).fillna(method='ffill') or: p_s.astype(np.float32).fillna(method='ffill') works well: 2015-07-24 47.96875 2015-07-25 47.96875 2015-07-26 47.96875 2015-07-27 47.15625 2015-07-28 47.96875

Expected Output

p_s..fillna(method='ffill') Out: 2015-07-24 47.96875 2015-07-25 47.96875 2015-07-26 47.96875 2015-07-27 47.15625 2015-07-28 47.96875 dtype: float16

Output of pd.show_versions()

[paste the output of ``pd.show_versions()`` here below this line] 1) On WINDOWS INSTALLED VERSIONS ------------------ commit: None python: 3.6.3.final.0 python-bits: 64 OS: Windows OS-release: 10 machine: AMD64 processor: Intel64 Family 6 Model 58 Stepping 9, GenuineIntel byteorder: little LC_ALL: None LANG: None LOCALE: None.None pandas: 0.20.3 pytest: 3.2.1 pip: 9.0.1 setuptools: 36.5.0.post20170921 Cython: 0.26.1 numpy: 1.14.0 scipy: 1.0.0 xarray: None IPython: 6.1.0 sphinx: 1.6.3 patsy: 0.4.1 dateutil: 2.6.1 pytz: 2017.2 blosc: None bottleneck: 1.2.1 tables: 3.4.2 numexpr: 2.6.2 feather: None matplotlib: 2.1.0 openpyxl: 2.4.8 xlrd: 1.1.0 xlwt: 1.3.0 xlsxwriter: 1.0.2 lxml: 4.1.0 bs4: 4.6.0 html5lib: 0.9999999 sqlalchemy: 1.1.13 pymysql: None psycopg2: None jinja2: 2.9.6 s3fs: None pandas_gbq: None pandas_datareader: None 2) On UBUNTU 16.04 INSTALLED VERSIONS ------------------ commit: None python: 3.6.2.final.0 python-bits: 64 OS: Linux OS-release: 4.4.0-108-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: ru_RU.UTF-8 LOCALE: ru_RU.UTF-8 pandas: 0.22.0 pytest: 3.2.1 pip: 9.0.1 setuptools: 36.5.0.post20170921 Cython: 0.26.1 numpy: 1.14.0 scipy: 1.0.0 pyarrow: None xarray: None IPython: 6.1.0 sphinx: 1.6.3 patsy: 0.4.1 dateutil: 2.6.1 pytz: 2017.2 blosc: None bottleneck: 1.2.1 tables: 3.4.2 numexpr: 2.6.2 feather: None matplotlib: 2.0.2 openpyxl: 2.4.8 xlrd: 1.1.0 xlwt: 1.3.0 xlsxwriter: 0.9.8 lxml: 3.8.0 bs4: 4.6.0 html5lib: 0.999999999 sqlalchemy: 1.1.13 pymysql: None psycopg2: None jinja2: 2.9.6 s3fs: None fastparquet: None pandas_gbq: None pandas_datareader: None

Comment From: jreback

float16 have almost no support anywhere as a first class type.

Comment From: jreback

we have a master issue about this

Comment From: gustavz

So this issue won't be addressed in future updates?

Comment From: jreback

see #9220

it would take pull requests from the community pandas is all volunteer and there are 3000 issues open